Your Baby at Week 12

At a Glance

During week 8, your baby’s intestines were infringing on umbilical cord space. But now they’re all set to move back into her abdomen, which they'll start to do in the next week.

Future Grandma

Your baby's pituitary gland at the base of the brain has begun producing hormones, meaning she'll be able to have babies of her own one day.

Germ Fighter

Your baby’s bone marrow is making white blood cells, so she’ll be able to fight off all those germs passed around the playground.

By now your baby weighs a full half-ounce, with a crown-to-rump length of two- to two-and-a-quarter inches — about the size of a small plum. It's hard to believe (especially from the outside, since you're probably barely showing at this point), but your baby has more than doubled in size during the past three weeks.

Baby’s Digestive System Begins Working

This week marks a turning point for your baby. At 12 weeks pregnant, the Herculean task of developing new bodily structures is nearing an end, as most of your baby's systems are fully formed – though there's still plenty of maturing to do. Now comes the maintenance phase, during which your fetus' systems continue to evolve for the next 28 weeks and the organs get to work. For one thing, the fetal digestive system is beginning to flex its muscles — literally — as it starts practicing contraction movements, a skill your little peanut will need after birth to push food through the digestive tract. The bone marrow is busy making white blood cells — weapons that will one day help your baby fight infection (including all those germs passed around the play group) once he's out of your safe haven. And the pituitary gland at the base of the brain has started producing the hormones that'll enable him to make babies of his own in a few decades or so.

Fetal Heartbeat

If you haven't already had the pleasure, it's likely that at this month's checkup you'll finally hear your baby's fetal heartbeat — a sound that will make your heart race with joy!

It’s a landmark week for your little one, since most of his key body systems and vital organs are fully formed by now. Your baby will spend the rest of his gestation bringing those systems up to speed and full maturation so they’ll be able to function to perfection once his big birth-day arrives.

Your fetus can now boast the achievement of having more than doubled in size in just three weeks. Crown-to-rump length is about two and a half inches, so he’s about the size of a kiwi, but weighs a lot less — just half an ounce. A fair amount of heft is in that crown: basic brain structure is complete and now it’s time for that brain mass to rapidly increase.

Your baby’s thyroid is now fully formed, the pituitary gland has started producing hormones, and the pancreas has begun to synthesize insulin. Not to be outdone, your baby’s bone marrow is churning out white blood cells, the critical weapons needed to fight infection once your little warrior is on the outside and no longer protected by your immune system.

Muscles in the digestive tract are getting primed, practicing their contractions so they can process food…and lots and lots of poop…after birth. And even though much of the small intestines are still folded up in storage in the umbilical cord, the villi — tiny, finger-like projections that absorb nutrients from food — are now in place.

The best development of all? If you haven’t already heard it, this is the week that your cutie’s heartbeat will come through loud and clear at your checkup. And that’ll music to your ears.

Your Body at Week 12

Dizzy Spells

As you near the end of your first trimester, your uterus, now about the size of a large grapefruit, begins to migrate from the bottom of your pelvis to a front-and-center position in your abdomen. If you're lucky, this will bring an end to one pesky early pregnancy symptom: the constant urge to urinate. Also slated to diminish somewhat now that you're on the cusp of your second trimester are some of those other early pregnancy symptoms: nausea, super tender breasts and nipples, food aversions and fatigue. But don't look now (though considering the symptom, maybe you should), there's a new one added to the mix: dizziness.

And guess who's to blame? Yup — it's your old friend progesterone again, which causes your blood vessels to relax and widen around 12 weeks pregnant, increasing the flow of blood to your baby (again, good for baby), but slowing the return of blood to you (as always, not so good for mom). What that means for you is lower blood pressure and reduced blood flow to your brain. These factors can contribute to that light-headed, dizzy feeling — especially when you get up too quickly — which is why slow and steady wins the race here. Another cause of dizziness during pregnancy is low blood-sugar levels, which can occur if you're not eating regularly. So don't try to run…or even walk…on empty. Here's a quick tip: If you feel dizzy or faint, lie down or sit with your head lowered between your knees, take deep breaths and loosen any tight clothing (like that button on your jeans you struggled to close in the first place). As soon as you feel a little better, get something to eat and drink.

Dealing with Low Sex Drive

Your best friend says being pregnant turned her into a sex kitten — but you feel more like a dead fish (and just about as bloated…which makes you feel even less sexy). What's the deal with your sex drive? Hormones hit every woman differently, turning up the heat for some and throwing ice water on others. Pregnancy symptoms can also stand between you and a good time — after all, it's hard to purr when you're busy gagging on dinner, get busy when you barely have the energy to get undressed or let your partner take advantage of those extra large breasts when you have a strict look-but-don't-touch policy in effect (ouch!). Rest assured, whatever you’re feeling is normal. Just stay emotionally connected with your partner and remember that many women who've lost that lovin' feeling in the first trimester get it back in the second in spades. So don't be surprised if a very warm front moves into your bedroom soon.

Pregnancy Symptoms Week 12

That gotta-go feeling may finally be starting to wane. But be sure to practice your Kegel exercises throughout the next several months to help prevent pregnancy-induced incontinence down the line. Read More

Be sure to eat regularly throughout the day — skipping meals causes low blood sugar, which can trigger headaches. Also, remember that it’s usually okay to take acetaminophen during pregnancy (but make sure your medical practitioner gives you the go-ahead first). Read More

If your nose knows a little too much lately (you can tell what your hubby ate for lunch the moment he walks in the door), try opening the windows. Or keep a lemon wedge nearby and sniff it when you start to smell a nausea-inducing odor — citrus can quell queasiness. Read More

Throughout this first trimester your body is working overtime to build the placenta, which is likely zapping your energy. So let yourself rest when you feel the need and take advantage of any opportunities to sleep now — before your baby arrives and demands 3 a.m. feedings. Read More

One way to decrease this embarrassing pregnancy symptom is to slow down when you eat. Scarfing down food can cause you to swallow air, which creates gas pockets in your already-overtaxed belly. Read More

Tips for You This Week

All pregnant women are with child sometime during flu season (October to May), which is why the CDC recommends all moms-to-be get vaccinated. Being pregnant doesn’t up your risk for shot side effects, notes a recent study.

Start doing your Kegels! Squeeze the pelvic floor muscles for up to 10 seconds, shooting for 3 sets of 20 a day. Building these bladder- and uterus-supporting muscles reduces your chance of bladder issues and eases a host of other pregnancy and postpartum symptoms.

Recommended Products

Just so you know, What to Expect may earn commissions from the shopping links included on this page.

From the What to Expect editorial team and Heidi Murkoff, author of What to Expect When You’re Expecting. Health information on this site is based on peer-reviewed medical journals and highly respected health organizations and institutions including ACOG (American College of Obstetricians and Gynecologists), CDC (Centers for Disease Control and Prevention) and AAP (American Academy of Pediatrics), as well as the What to Expect books by Heidi Murkoff.